We Are All Brains in Vats

The Matrix made all of us ask the same disturbing questions: How do I know that the world I see, hear, and touch is real? Can I prove that I’m not actually in a pod created by machines bent on harvesting my bioelectricity?

These unsettling questions are related to a thought experiment called “The Brain In a Vat” problem. The thought experiment was originally proposed by one of my old advisors at Princeton, Gilbert Harman. It’s an updated version of Descartes’ “Evil Demon” thought experiment, which asks whether the world we perceive is an illusion. Given the possibility that the world is an illusion, all we can know for sure is that our thoughts exist: “I think therefore I am.”

“Our visual cortex may create the experience of light, but the cortex itself is wrapped in complete darkness…”

The “brain in a vat” scenario makes this frightening possibility biologically plausible. Imagine that a mad scientist takes out your brain and puts it in a vat with life-sustaining liquid. The scientist then connects your brain via wires to a supercomputer, and the supercomputer provides electrical impulses to your brain that are indistinguishable from those that your brain normally receives from your nerves. If the supercomputer could accurately simulate your world, then you would have no idea that nothing you perceive is real.

The “brain in a vat” idea opens up some troubling philosophical questions, but for me it also drives home just how remarkable the brain is. Our brains are, literally, in vats. They float inside our skulls, surrounded by about 0.15 liters of cerebrospinal fluid, and they receive complex patterns of stimulation from the sensory nerves that enter our skull. The brain takes these patterns of stimulation and turns them into a sensory universe so complex and vivid that we forget that it is, at best, only a representation of the outside world.

Think about it this way. Our visual cortex may create the experience of light, but the cortex itself is wrapped in complete darkness, shielded by our skull from any actual light. All it can do is receive information about light outside of our skull. What’s astounding is that the brain can turn this information into experience!

The brain in a vat thought experiment reveals that the information our brain receives could be made up. And if that information is made up, then the brain would turn that made up information into a false sensory world – like The Matrix. I’ll let philosophers puzzle over what this means for our certainty about the outside world. As a neuroscientist, I’m still hung up on the incredible fact that the brain is even capable of turning information – whether accurate or made up – into experience.

So, yes, we are brains in the vats of our skulls – and that is breathtaking.


Illustration by Jooyeun Lee.


Harman, G. (1973). Thought. Princeton University Press.


Daniel Toker is a neuroscience PhD student at the University of California, Berkeley, specializing in computational and cognitive neuroscience. In his research, he uses information theory and graph theory to characterize what the brain is doing when it's conscious, and what changes when it's not. Before coming to Berkeley, Daniel studied philosophy and neuroscience at Princeton University. His other science writing can be found on the following social media platforms: Instagram: @the_brain_scientist, Twitter: @daniel_toker, Website: danieltoker.com.

3 thoughts on “We Are All Brains in Vats

  • July 3, 2017 at 5:40 am

    But we might not be “brains in vats.” Maybe we are actually purple slugs and VALIS is beaming information into our little slug brains. It *could* be…who gives a s*&^? Indirect realism is as conceptually-bankrupt as it is popular – just like the notion that brains are “information processors.” That view is just another kind of homunculistic nonsense – just like indirect realism. Though I do not agree with everything Bennett & Hacker say, I am glad that they said what they did about the mereological fallacy. Cognitive psychology and cognitive neuroscience are jokes.

  • February 1, 2018 at 8:53 am

    can we use that tiny amount electricity { which everyone has in the body } to generate large amount of electricity and actually transfer it out of our brain , thus creating natural electric field around that person ? …. hence that person can move stuffs with the help of electric field generated around him/her ! , I know it’s hypothetical ….or is it possible ?

  • August 3, 2018 at 12:40 am

    I agree with the author: independent of the causal antecedents of our brain’s inputs, the fact that our brain transduces whatever information is coming in, into the rich world of our sensory modalities, is amazing. It’s interesting, also, to consider taking the same idea a bit further.
    Our concept, or *experience* of spatial location and dimension (put special relativity aside for a moment, just consider space as 3-space) is one we ought to include as at least significantly “manufactured”, like auditory tones, light and color, etc.
    How so? Proprioception. The propioceptive sensory system gives us… after transduction by the brain … the feel of close, further away… the spacy-ness of the space around us. Close your eyes and move your arms and hands around. What to you *experience*? That is proprioceptive qualia, or proprioceptive sensation.
    What is “real” space, like? Might it be as different as electromagnetic energy (as modeled by the physicist) is different from our experience of it… our “false color” discrimination of the visible spectrum?
    So, what IS out there? Uniting the worlds of physics, and sensory/cognitive phenomenology is still one of the great frontiers. I will think about it until either I understand it, or lose my lucidity in old age

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